A phase retarder is a type of optical element changing the polarization state of light passing through the same, and equally said a wave plate. When a light passes through an electromagnetic phase retarder, the polarization direction (direction of electric field vector) becomes a sum of two elements (an ordinary ray and an extraordinary ray) parallel or perpendicular to the optic axis, and changes after passing the phase retarder because the vector sum of two elements varies according to the birefringence and the thickness of the phase retarder.
Recently, one of big issues of preparing optical film which can be used to the phase retarder is to prepare a high performance film at a small charge. Because, when liquid crystal compounds having high birefringence are used for preparing an optical film, it is possible to realize the necessary retardation value with small quantity of liquid crystal compounds. And, when such liquid crystal compounds are used, it is possible to prepare a thinner folial film.
Therefore, many studies for obtaining the liquid crystal compounds having high birefringence have been carried out actively, but there was a limitation on applying them to the industry in practice because of the orientation problem of the membrane when prior liquid crystal compounds were coated on a film.